A number of ultracompact H ii regions in Galactic star forming environments have been observed to vary significantly in radio flux density on timescales of 10–20 years .
Theory predicted that such variations should occur when the accretion flow that feeds a young massive star becomes unstable and clumpy .
We have targeted the massive star-forming region W49A with the Karl G. Jansky Very Large Array ( VLA ) for observations at 3.6 cm with the B-configuration at \sim 0 \farcs 8 resolution , to compare to nearly identical observations taken almost 21 years earlier ( February 2015 and August 1994 ) .
Most of the sources in the crowded field of ultracompact and hypercompact H ii regions exhibit no significant changes over this time period .
However , one source , W49A/G2 , decreased by 20 % in peak intensity ( from 71 \pm 4 mJy/beam to 57 \pm 3 mJy/beam ) , and 40 % in integrated flux ( from 0.109 \pm 0.011 Jy to 0.067 \pm 0.007 Jy ) , where we cite 5 \sigma errors in peak intensity , and 10 % errors in integrated flux .
We present the radio images of the W49A region at the two epochs , the difference image that indicates the location of the flux density decrease , and discuss explanations for the flux density decrease near the position of W49A/G2 .